The statements in this section merely provide background information related to the present disclosure. Accordingly, such statements are not intended to constitute an admission of prior art.
Engine control includes control of parameters in the operation of an engine based upon a desired engine output, including an engine speed and an engine load, and resulting operation, for example, including engine emissions. Parameters controlled by engine control methods include air flow, fuel flow, and intake and exhaust valve settings.
Boost air can be provided to an engine to provide an increased flow of air to the engine relative to a naturally aspirated intake system to increase the output of the engine. An air charging system such as a turbocharging system utilizes pressure in an exhaust system of the engine to drive a compressor providing boost air to the engine. Exemplary turbochargers can include variable geometry turbochargers (VGT), enabling modulation of boost air provided for given conditions in the exhaust system. A supercharger utilizes mechanical power from the engine, for example as provided by an accessory belt, to drive a compressor providing boost air to the engine. Engine control methods control boost air in order to control the resulting combustion within the engine and the resulting output of the engine.
Exemplary engines may utilize two-stage air charging or boosting wherein a secondary air charger is utilized to increase air flow to the engine. The secondary air charger may be an electric powered air charger or e-boost. Methods of controlling an engine having two-stage boosting varies from the control methods of a single-stage boosted engine. The control may be achieved using unique model based control of the electric air charging system.
Exhaust gas recirculation (EGR) is another parameter that can be controlled by engine control methods. An exhaust gas flow within the exhaust system of an engine is depleted of oxygen and is essentially an inert gas. When introduced to or retained within a combustion chamber in combination with a combustion charge of fuel and air, the exhaust gas moderates the combustion, reducing an output and an adiabatic flame temperature. EGR can also be controlled in combination with other parameters in advanced combustion strategies, for example, including homogeneous charge compression ignition (HCCI) combustion. EGR can also be controlled to change properties of the resulting exhaust gas flow. Engine control methods control EGR in order to control the resulting combustion within the engine and the resulting output of the engine. EGR system circuits can include multiple routes of providing exhaust gas into the combustion chamber including high pressure exhaust gas recirculation circuits and low pressure exhaust gas recirculation circuits. In boosted engines, exhaust gas may be directed into the engine intake manifold via a high pressure route wherein the exhaust gas is directed back into the intake flow prior to flowing through the VGT such that the exhaust gas remains pressurized. The exhaust gas may additionally be directed back to the engine intake manifold through a circuit after passing through the VGT, at which point the exhaust gas is no longer under pressure.
Air handling systems for an engine manage the flow of intake air and EGR into the engine. Air handling systems must be equipped to meet charge air composition targets (e.g. an EGR fraction target) to achieve emissions targets, and meet total air available targets (e.g. the charge flow mass flow) to achieve desired power and torque targets. The actuators that most strongly affect EGR flow generally affect charge flow, and the actuators that most strongly affect charge flow generally affect EGR flow. Therefore, an engine with a modern air handling system presents a multiple input multiple output (MIMO) system with coupled input-output response loops.
MIMO systems, where the inputs are coupled, i.e. the input-output response loops affect each other, present well known challenges in the art. An engine air handling system presents further challenges. The engine operates over a wide range of parameters including variable engine speeds, variable torque outputs, and variable fueling and timing schedules. In many cases, exact transfer functions for the system are unavailable and/or the computing power needed for a standard decoupling calculation is not available. Multi-route EGR operation allows the system to run higher EGR rates at higher boost levels, but affects the VGT/compressor flow and power which impacts boost control design and performance.